The present invention relates to reaction rate detection systems and more particularly to such systems employed for photometric analysis of reaction rate of enzyme activity.
With certain types of solutions, it is important to determine the rate of change or reaction rate of the solution in the presence of certain catalysts. For example, placing an enzyme in certain types of solutions will cause a chemical reaction to occur. The enzyme acts as a catalyst and causes the reaction, but it does not enter into the reaction. However, the rate of change or reaction rate of the solution does indicate enzyme activity and enzyme activity is a measure of the enzyme concentration.
With certain types of enzyme reaction rate photometric analysis, the light absorbance of an enzyme reaction within a cell is continuously monitored at a predetermined light frequency and the electrical output of a photomultiplier or other photodetector is recorded. A technician then can perform a differentiation in order to determine the reaction rate or it may be performed by a computer. Circuitry which can provide a continuous differentiation function in response to an electrical signal can be provided. However, it is complex and expensive.
In the foregoing type of analysis, it is possible for the electrical photodetector signal to exhibit variations and discontinuities. For example, such results can occur when a measurement is taken before the reaction has stabilized at a constant rate. Furthermore, depending upon the type of reaction, the reaction rate may follow a linear pattern initially and then diverge from the linear pattern. Signals exhibiting these variations must be identified so that they may be discarded and/or the test terminated and a new test initiated. As with the reaction rate determination this type of analysis has been performed by a technician or a computer. Circuits which have been heretofore available for performing these functions have performed them on a continuous basis. Most commonly a differentiating circuit identical to the previously noted differentiating circuit is employed. As noted above, such circuits are complex and expensive.
Generally in systems performing the above-noted analysis a calibration is provided. The calibration allows the system to provide an output directly readable in terms of known units of measurements such as absorbance units (ABS) or international units (I/U). When such calibrations are provided, the analysis requires particular volumes of solution and enzyme, and generally a particular reaction temperature. It is not possible to use different volumes or different temperatures without entirely recalibrating the system.